In vertebrate animals, the heart is a hollow muscular organ having four pumping chambers: the left and right atria and the left and right ventricles, each provided with its own one-way valve. The natural heart valves are identified as the aortic, mitral (or bicuspid), tricuspid and pulmonary, and are each mounted in an annulus comprising dense fibrous rings attached either directly or indirectly to the atrial and ventricular muscle fibers. Each annulus defines a flow orifice. The four valves ensure that blood does not flow in the wrong direction during the cardiac cycle; that is, to ensure that the blood does not back flow through the valve. Blood flows from the venous system and right atrium through the tricuspid valve to the right ventricle, then from the right ventricle through the pulmonary valve to the pulmonary artery and the lungs. Oxygenated blood then flows through the mitral valve from the left atrium to the left ventricle, and finally from the left ventricle through the aortic valve to the aorta/arterial system.
The mitral and tricuspid valves are defined by fibrous rings of collagen, each called an annulus, which forms a part of the fibrous skeleton of the heart. The annulus provides peripheral attachments for the two cusps or leaflets of the mitral valve (called the anterior and posterior cusps) and the three cusps or leaflets of the tricuspid valve. The native valve leaflets flex outward when the valve opens and their free edges come together or coapt in closure.
The free edges of the mitral leaflets connect to chordae tendineae from more than one papillary muscle. Mitral valve malfunction can result from the chordae tendineae (the chords) becoming stretched, and in some cases tearing. Also, a normally structured valve may not function properly because of an enlargement of or shape change in the valve annulus. This condition is referred to as a dilation of the annulus and generally results from heart muscle failure. In addition, the valve may be defective at birth or because of an acquired disease. From a number of etiologies, mitral valve dysfunction can occur when the leaflets do not coapt at peak contraction pressures. As a result, an undesired back flow of blood from the left ventricle into the left atrium can occur.
Various surgical techniques may be used to repair a diseased or damaged valve. A commonly used repair technique effective in treating incompetence is annuloplasty, which often involves reshaping the annulus by attaching a prosthetic annuloplasty repair segment or ring thereto. For instance, the goal of a posterior mitral annulus repair is to bring the posterior mitral leaflet forward toward to the anterior leaflet to better allow coaptation. The annuloplasty ring is designed to support the functional changes that occur during the cardiac cycle: maintaining coaptation and valve integrity to prevent reverse flow while permitting good hemodynamics during forward flow.
The annuloplasty ring typically comprises an inner substrate or core of a metal such as a rod or multiple bands of stainless steel or titanium, or a flexible material such as silicone rubber or polyethylene terephthalate (PET) (e.g., Dacron® PET, Invista, Wichita, Kans.) cordage, covered with a biocompatible fabric or cloth to allow the ring to be sutured to the fibrous annulus tissue. More rigid cores are typically surrounded by an outer cover of both silicone and fabric as a suture-permeable anchoring margin. Annuloplasty rings may be stiff or flexible, and may have a variety of shapes in plan view, including continuous oval, circular, D-shaped, or kidney-shaped, or discontinuous C-shaped, sometimes referred to as a band. Examples are seen in U.S. Pat. Nos. 5,041,130, 5,104,407, 5,201,880, 5,258,021, 5,607,471 and, 6,187,040. Most rigid and semi-rigid annular rings for the mitral valve have a kidney-like or D shape, with a curved posterior segment co-extensive with the posterior valve leaflet, and a somewhat straighter anterior segment co-extensive with the anterior valve leaflet.
One popular annuloplasty ring is the partially flexible Carpentier-Edwards Physio® ring available from Edwards Lifesciences of Irvine, Calif. The Physio® ring is a “semi-rigid” ring because it offers selective flexibility at the posterior section while preserving the remodeling effect through a rigid anterior section. The newer Physio II® ring from Edwards Lifesciences also features up and down curves to better fit the nonplanar contours of the mitral annulus. Various other rings have posterior bows, e.g., U.S. Pat. Nos. 6,805,710 and 6,858,039, 7,959,673, or other three-dimensional configurations.
Despite numerous designs presently available or proposed in the past, there is a need for an annuloplasty ring that better accounts for the native mitral annulus anatomy.